1. Field of the Invention
The disclosed concept relates generally to a mandrel assembly coupled to a mandrel carrier for decorating a container and, more specifically, to a mandrel assembly wherein the mandrel is self-aligning to the surface of the can decoration device.
2. Background Information
Decorations, i.e. any indicia, are typically applied to a can by a can decoration device that utilized a rotating “blanket.” The blanket, or more typically a plurality of blankets, are disposed on the circumference of a large diameter rotating disk, i.e. large diameter relative to the can body to which the can decoration is applied. One or more ink stations apply ink in a desired pattern to the blankets prior to the blankets contacting the cans. The cans are made to rotate at a speed corresponding to the blanket and then brought into contact with the blanket. The can is in contact with the blanket for substantially one full rotation of the can. During the period in which the can and blanket contact each other, the ink is transferred from the blanket to the can. The can may then be subjected to further treatments, e.g. varnish, drying, etc., to ensure the ink does not smudge.
The device used to support and manipulate the cans during the can decoration procedure is a mandrel turret. Generally, the mandrel turret includes a disk having an axis of rotation. The mandrel turret disk axis of rotation is substantially parallel to the axis of rotation of the blanket wheel. A plurality of elongated mandrel assemblies are coupled to the mandrel turret disk. Each mandrel assembly longitudinal axis is generally parallel to the axis of rotation of the blanket wheel and the mandrel turret disk axis of rotation, however, if the mandrels need to have a certain amount of radial “toe-in,” as described below, the mandrel turret disk axis of rotation may be angled toward the blanket wheel axis.
As noted above, the can must be rotating as it contacts an inked blanket. This rotation is accomplished by the mandrel assembly upon which the can is mounted. It is initially noted that at this point in the manufacture of the can, the can is incomplete, i.e. the can does not have a top. Thus, the can is, essentially a cup having a generally planar base with a depending sidewall. The can is disposed over the distal end of the mandrel assembly and held in place by a vacuum. That is, the mandrel assembly is structured to draw a vacuum at the distal end whereby a can is held in place.
To effect the rotation of the can, the mandrel assembly includes a mandrel and a mandrel shaft. Both the mandrel and the mandrel shaft are generally cylindrical, but have portions with different radii. The mandrel shaft includes a passage through which a vacuum may be drawn. One end of the mandrel shaft, the proximal end, is coupled to the mandrel turret disk. Thus, the mandrel shaft is cantilevered from the mandrel turret disk. Preferably, the mandrel shaft does not rotate relative to the mandrel turret disk (but does rotate about the mandrel turret disk axis as the mandrel turret disk rotates).
The mandrel is, generally, a cylindrical shell that is disposed over the mandrel shaft. The mandrel is generally open at both ends. The mandrel is structured to concentrically rotate about the mandrel shaft. A bearing assembly is disposed between the mandrel and the mandrel shaft. The bearing assembly allows the mandrel to rotate relative to the mandrel shaft. A rotation device, typically a system of belts coupled to the can decoration device blanket wheel to one or more mandrels, is structured to bring each mandrel to the proper rotational speed just before the can contacts the inked blanket. The rotation device is decoupled from the mandrel as, or just before, the can contacts the inked blanket. It is further noted that the mandrel must be a specific distance from the blanket so as to create the proper pressure between the can and the inked blanket that causes the ink to transfer without distorting the blanket thereby causing a distorted image or causing the mandrel, and therefore the can, to slow its rotational speed, which also causes a distorted image on the can.
In this configuration, the various components of the can decoration device and the mandrel turret disk must be precisely aligned and structured to rotate at specific speeds to ensure the can decoration is applied to the cans without smudging, blurring or otherwise distorting the indicia. Accordingly, the elements of the mandrel turret disk are traditionally very rigid so as to control their position relative to other elements.
Still, even with very rigid components, one cause of misalignment is the fact that the mandrel assembly is cantilevered. In this configuration, the distal end of the mandrel assembly is known to deflect in response to the pressure applied thereto by the blanket at the time of applying the image to the can. One method of compensating for this deflection is to construct the mandrel assembly with a selected radial displacement, or “toe-in,” of the mandrel assembly. That is, the mandrel turret disk is tilted radially toward the blanket wheel. This causes the distal end of the mandrel assembly to be located closer to the blanket wheel axis of rotation than the proximal end of the mandrel assembly. Thus, when the blanket contacts the can (on the mandrel), the bias created by the blanket causes the mandrel assembly to deflect inwardly a slight amount whereby the longitudinal axis of the mandrel assembly is substantially parallel to the axis of rotation of the blanket wheel.
It is noted that, as part of the rigid construction of a mandrel assembly, and as shown in FIG. 1, there are typically two sets of bearings 2, 3 disposed between the mandrel 4 and the mandrel shaft 5. There is usually a ball bearing assembly 2 disposed adjacent the distal end of the mandrel assembly and a needle bearing 3 assembly disposed adjacent the proximal end of the mandrel assembly. By supporting the mandrel on the mandrel shaft at two locations along the longitudinal axis of the mandrel assembly, the mandrel, while rotatable, is in a fixed orientation relative to the mandrel shaft.
Thus, in order to get consistent and good quality can decoration of all cans, each mandrel assembly must be significantly parallel to the axis of rotation of the blanket wheel. Any out of parallel condition on the part of a mandrel assembly can result in every can on that mandrel assembly not being fully printed. When this happens, it is necessary to determine which part in the related mandrel assembly is out of specification and replace it. This can result in a significant amount of machine downtime. Sometimes when an operator detects such a misalignment, rather than perform the proper maintenance, the operator will simply increase the can decoration device pressure in order to get the out-of-specification mandrel assembly to print properly. This, however, results in higher than necessary loading of the remaining mandrel assemblies and causes reduced service life of the mandrel turret disk assembly in general.